I like the oil filled heaters when have shore power. We keep one running in the back bathroom at home during the winter.
I have used them in my van with shore power and works well. With the aforementioned caveat of being big and bulky. Also mine does not have a thermostat, so frequently wake up either to hot or to cold.
I'll second Wallowa on the buddy heaters. They may have improved in the last 10 yrs. But about that long ago, I tried one in the van for a few nights with outside temps in the 20's. With the front windows cracked 2", it still set of my carbon monoxide alarm, And I felt light headed.
